Investigating the hot gas in active brightest cluster galaxies

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Abstract

We investigate a crucial phase in the cooling–feedback cycle in the star forming Brightest Clus-
ter Galaxies (BCGs) by looking at the optical emission line properties of the reheated gas that
ultimately causes the cycle to repeat. We investigate the source, or the mixture of sources, of ion-
ization of the gas. To identify the dominant ionization processes, excitation sources, morphology
and kinematics of the hot gas, line ratios over the entire optical wavelength range are necessary.
For this purpose, the spatially–resolved spectra over the entire optical wavelength range for eight
nearby, active BCGs in X–ray luminous groups and clusters have been obtained with the South-
ern African Large Telescope (SALT). The BCG sample was chosen to have H
α
detections – a
strong indication of star formation activity, as well as existing hot cluster data from X–ray regime
available. The fundamental gas properties such as electron density, gas temperature, metallic-
ity and several abundances were derived using the spectral features across the long wavelength
range. The present optical data will be combined with the other multi–wavelength data to form a
complete view of the di
ff
erent phases (hot and cold gas and young stars) and how they interact in
the processes of star formation and feedback detected in central galaxies in cooling flow systems,
as well as the influence of the surrounding intracluster medium (ICM). Here we present our pre-
liminary results on one of those eight BCGs, Hydra A, which shows the complexity and spatial
variation of the ionization mechanisms in the nucleus